1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to packaging of a semiconductor device by use of a ceramic package.
2. Description of Related Art
A ceramic package is superior in material characteristics such as electric insulation, thermal conduction, thermal expansion, mechanical strength and chemical stability. Further, since the economical mass production process of the ceramic package has been established, the ceramic package is widely used in the semiconductor integrated circuit field.
A conventional semiconductor device using such a ceramic package will be described below with reference to FIG. 1. First, original ceramic plates which are called green sheets (three green sheets in the figure) are formed and then via-holes for wiring and an opening for mounting a semiconductor element are formed for each of the green sheets other than one to form internal package wirings. Next, the plurality of green sheets are laminated and baked to form a ceramic package 21. External leads 23 are soldered to the baked ceramic package, and planting is performed for completion of the ceramic package 21. A semiconductor element 25 is mounted to a recession section of the ceramic package as a semiconductor element mount section by metal solder 26. The mounted semiconductor element 25 and the ceramic package 21 are connected by metal wires 28 made of metal such as aluminum (Al) or gold (Au) for electric connections. The ceramic package 21 shown in FIG. 1 is formed through the above processes. Further, the ceramic package is sealed and a semiconductor device is completed.
In the above conventional process of forming the ceramic package, the green sheet shrinks 20 to 30% in the baking. Further, a common difference between a design size and an actual size of the opening such as the recession section is about 10% because of displacement between the green sheets generated when the green sheets are laminated. In addition, as shown in FIG. 2, in the process of assembling the semiconductor device, a space is required for a tool 29 to hold the semiconductor element 25 and to move to the recession section of the ceramic package 21 and a space is required to vibrate the tool 29 for fitting the semiconductor element 25 to the recession section. Therefore, the actual dimension of the recession section needs to be larger at least 2 mm than that of the semiconductor element 25.
As described above, in such a ceramic package type semiconductor device, because the metal wires between the semiconductor element 25 and the ceramic package 21 are long, there is a problem in that the number of semiconductor elements 25 are limited due to an inductive component of the metal wires and that the operation speed cannot be increased.